In centrifugal separators there is a need for efficient mechanical sealings in several different positions, i.e. mechanical sealings which are suitable for sealing a gap between a rotating separator part and a stationary separator part, or between two rotating separator parts rotating at different speeds, for instance in decanter centrifuges.
In for instance so-called hermetic centrifugal separators, mechanical sealing is required between the rotating centrifuge rotor and a stationary inlet and/or outlet pipe extending into the centrifuge rotor. Furthermore, one or several mechanical seals are required between a stationary connection housing and a rotating inlet and/or outlet pipe connected to and communicating with the interior of the centrifuge rotor.
One problem with available mechanical seals is to provide a sufficient abutment force between the two contact surfaces so that an efficient sealing of the gap is achieved during all operating conditions. A further problem with available mechanical seals is the wear which they are subjected to. In particular, when the centrifugal separator is started and before any liquid is available at the mechanical seal, the contact surfaces of the seal will slide against each other in a dry state, which results in high wear. In order to solve this problem, expensive equipment is required for supplying sealing liquid to the mechanical sealing. In many applications, such as at separation of food products, there are at the same time high hygienic requirements. It is therefore necessary to be able to simultaneously clean all surfaces which are in contact with the product through a so-called Cleaning In Place, CIP.
U.S. Pat. No. 4,846,728 discloses a centrifugal separator comprising a first stationary separator part in the form of a stationary casing and a second separator part, which comprises a centrifuge rotor. The centrifuge rotor is non-rotating during a rest state and rotates during operation about an axis of rotation at a determined speed in relation to the stationary casing. A space is provided in connection to the casing and the centrifuge rotor and houses, during operation, a rotating liquid body which contains a medium. A mechanical sealing device is provided at the space for sealing of the space. The mechanical sealing device comprises a first sealing element, which is provided on the casing and has a first contact surface, and a second sealing element, which is provided on the centrifuge rotor and has a second contact surface which is parallel to the first contact surface. The first contact surface and the second contact surface are arranged to abut each other during operation. The mechanical sealing device is designed in such a way that the rotating body during operation state on the second sealing element in such a way that the second contact surface is pressed against the first contact surface with an abutment force.